When you say you do not have the original unlock code is this the from original setup?

Also, in certain upgrades the original sim/account is needed that the device was originally setup with to continue the upgrade, you can reach this point without bricking the device.

Usually an official update will not brick a device. However backup everything first always.

If the device is unlocked, it should remain unlocked following the update although this does depend on how the device was unlocked, legally = should be fine, illegally = might get patched within update.

Ensure you have enough storage available, enough battery, and it is recommended to update whilst connected to a VPN. You can setup an Express VPN trial for 7 days to do this update.

Once connected to a VPN go to settings > about device > update/software update and update via that menu to update the OS. You should not recieve any SMS with update links only via the official update menu/notifications that appear.

Hope that helps a little.
Either way back everything up, and proceed at your own risk. I am not responsible for any damage, moreso it would be the manufacturers fault should you have followed the correct standard procedure to update the OS

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